What Was the Name of that Book? Part Three

This book is probably easily findable, if I had a bit more information (as most of my questions are, I guess.)

I didn't read this whole book. I picked it up at a booksale and thumbed through it. I didn't buy it, but I'd read enough of it to be curious about it. It was a paperback, possibly had a red cover. I think it was geared to adults, possibly a teen title but more likely adult. I think the parents were splitting up and their teenage daughter was pregnant, but she was overweight and had been hiding it, I think even from the baby's father, who might have been a friend of hers? The teen's voice was sarcastic and I think she was a first-person narrator, at least for part of the book. 

Does anyone remember this book but me?